The relationship between weather and plant growth has been recognized for many centuries. For example, the importance of inter-annual variations of weather conditions for resulting differences in plant development levels is well-known. The understanding of the relationship of weather to plant and animal growth, known as phenology, has become an important process in annual estimation of crop stages, pest emergence, and disease development. Modern phenology began with recordings of plant and insect development in relation to climate conditions, and over the past fifty years, the development of phenological models has accelerated to provide crop-specific models, and even crop variety-specific models. The models, which are commonly referred as growing degree day (GDD) models, have been developed to understand the timing between accumulated growing degrees and stages of crop development. Combined with pest and disease emergence, which are also phenological processes, the growing degree day models permit producers and crop advisors to make critical decisions on crop protection and enhancement.
Growing degree day models, whether specifically for issues such as insects or diseases planning, or more generally for plant growth, were derived with the understanding that sensible heat derived from atmospheric temperatures drives metabolic processes, affecting the rate of growth and development. In simple terms, a growing degree day is an index of the amount of heat accumulated in a day to drive the metabolic process related to growth or development. Research in the past half-century has led to the establishment of mathematical equations that predict the rate of development at different temperatures for a large selection of crops, and for crop varieties. These mathematical equations are used to predict the rate of insect, disease, or plant development as temperatures fluctuate over time, and provide guidance on upcoming stages of growth and measures to respond to impacts of such growth.
Throughout the duration of a growing season, the speculation of final crop development maturity and the rate of crop development is an important consideration for a grower. From the time of planting and continuing through until the end of a growing season, the uncertainty of how a crop will mature, along with when and with what yield, are considerations of farmers when estimating final cash flows and determining the timing of inputs and actions to support crop development and farm business profitability. Traditional use of crop growth models, such as accumulated growing degree models, utilize accumulated weather conditions that have occurred from crop planting to the current date to provide a historical profile of development. Short-term weather forecasts are also used, but this provides only limited additional insight into crop development for near-term crop management decisions and does not provide a longer-range view of risks and expectations.
Therefore presently-used and known methods in modeling crop growth and development do not provide an adequate estimation of how a crop will develop over a longer range, such as through a remainder of the growing season. The application of climatological data for the crop's geographical region fails to provide anything more than a loose approximation as to development for the remainder of the growing season, since climatological data does not reliably represent a given year's daily conditions.